pigment

A natural or synthetic, organic or inorganic
substance that imparts color, as well as black and
white, and is used in the manufacture of paint,
printing inks, etc. A pigment is insoluble in its
liquid medium, and imparts its coloring effect
simply by spreading over the surface to which it
is applied. A pigment produced by precipitating a
dye on a colorless, or inert, base, thus rendering
the dye insoluble, is called aLAKE , while a
synthetic organic compound that is insoluble and
can be used directly as a pigment is called a
"toner."

Pigments are generally classified according to
their origin. Those produced by processing colored
earths are referred to as EARTH COLORS , while
those produced by chemical processes from
inorganic raw materials that are not in themselves
coloring matter are called artificial inorganic
pigments. The finest grades of earth colors occur
in specific areas, e.g., French yellow ochre,
Italian raw and burnt sienna, etc. Early pigments
included the native earths, e.g., red iron oxides
and yellow ochre, as well as manufactured
pigments, such as crimson lake, lampblack, and
white lead.

Pigments should be chemically inert, so as not to
react in an undesirable manner with other pigments
or liquids with which they may be mixed, and they
should also be lightfast and not fade or darken
when exposed to typical indoor lighting, such as
indirect sunlight, artificial light of normal
intensity, and controlled temperature and humidity
variations. All pigments of very high quality will
endure indefinitely under proper conditions,
although some may undergo loss of color if exposed
to direct sunlight. Cf: DYE . (17 , 195 , 233 )